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Conundrum

Thu May 24 2012, 07:49PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Actually there is a very simple way to get sub 0.01 mm accuracy on a RepRap.
Its so simple a child could build it with a simple quad of piezo speakers appropriately mounted and secured, 100V supply from HV852 and a pair of MPSA42's to serve as the adjustable voltage so that the speakers move precisely.
This works because even though the movement is 0.2mm at 100V its always the same no matter how many times you move the speaker.

The tricky part is to get that initial alignment, which uses a simple "bed of nails" optical grid projected from the top.

add to this please

-A

Weston

Thu May 24 2012, 08:10PM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

Being one of the 4hv members that actually owns a reprap (Mendel Prusa), I can say that accuracy is not an issue. Resolution is. And so is print speed.

An improvement I would like to see is an extruder that does not need standard round filament. Perhaps one that can use plastic strips generated from scrap material instead.

Thomas W

Thu May 24 2012, 08:50PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

i havent got one, but couldnt you make a home made extruder to make it from scraps?

AndrewM

Thu May 24 2012, 09:07PM

Registered Member #49 Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362

Weston wrote ...

Being one of the 4hv members that actually owns a reprap (Mendel Prusa), I can say that accuracy is not an issue. Resolution is. And so is print speed.

I do not agree, I think accuracy is paramount. Of course that includes resolution sufficient to achieve the required accuracy.

Of course, for me, this is irrelevant because I STILL have no fixed the hot end on mine :(

Thomas W

Thu May 24 2012, 09:49PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

with a bit of luck i may be getting some servo sliders, being repaced with ultra fast lineir motors on a assembly line, mabye il make a 3D printer :o

Weston

Thu May 24 2012, 10:48PM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

AndrewM wrote ...

Weston wrote ...

Being one of the 4hv members that actually owns a reprap (Mendel Prusa), I can say that accuracy is not an issue. Resolution is. And so is print speed.

Right now, the achievable accuracy is much greater than the achievable resolution. So accuracy will not be an issue for some time.

Not to mention that when accuracy of 0.01 inches or greater is wanted, the part will have to be kept at a constant temperature or the coefficient of expansion of the plastic will have to be very precisely measured due to thermal expansion/contraction. So there are significant obstacles besides just producing an accurate mechanical positioning system

Conundrum

Fri May 25 2012, 07:54AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

I still want to see someone do my suggested modification of an IR thermometer on the printhead so that the temperature of the plastic on both the workpiece and the filament can be totally controlled.

I agree that being able to use scrap plastic is very useful, in fact one way to do this would be an automated laser spectrometer to identify the plastic being recycled and sort it into bins accordingly.

Many defunct printers are mostly ABS, so these would be an idea feedstock.
Some food containers are also ABS or another similar plastic, or at least something which could be compressed down into a build plate.

Interestingly, many problems with the RepRap could be avoided if the printhead was swappable.
One way to do this would be to use magtrix connectors to hold the printhead in place so it could be selected automagically by the software from a bank of printheads.
This would mean that say, a silver printhead could be selected, or a laser etcher, or a photographic unit, 3D scanner, etc meaning a single build unit could do a dozen different tasks.

Another useful tip, make a magnetic solder variant of low melt 120-160 (1.6% In) using tin coated iron particles.
This would also allow salvaging of some through hole components.
Being able to select a SMD then heat the PCB with hot air, vacuum it up then insert it in a tray would also be handy.

An interesting idea I also came up with to help automate deposition of silver paint is to install a pager motor onto the container using Polymorph.
This ensures adequate mixing and reduces clumping to low levels, allowing a simple syringe based print head to be used.
Once printing is complete simply pick up some IPA to rinse out the head and drop it into a waste container for later reuse.

Has anyone explored electrowetting based printing yet?
Heating up the plastic from underneath via IR laser would also give the silver something to initially stick to, while providing structural reinforcement.

Not having a build system yet I am having to use manual methods to test these ideas, the guy who was also working on a RepRap over here seems to have essentially given up due to work pressures

Lesson learned, pay the $$$ and get something that works FIRST then modify that, not reinvent the wheel.
Had I known this I'd have used decent stepper controllers with idiotproof drivers.

Another useful tip is to only recycle components such as printer parts for the rails as a last resort if all else fails.
The cogs and other parts simply aren't accurate enough and are prone to falling apart due to accumulated microcracks.

Steve Conner

Fri May 25 2012, 09:56AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

For me, the biggest problem with the Reprap is that everything you make comes out looking like the Spaghetti Monster's noodly appendage. The movement of the print head might be accurate, but the laying down of the plastic is a splattery mess.

I do like Conundrum's interchangeable printhead idea, though.

Conundrum

Sat May 26 2012, 09:00AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Maybe one solution to this is to use a central core of low melting point alloy with an outer core of plastic?
Or a mixture of plastic and iron containing metal powders that fuse together with induction?

Neet Studio

Sat May 26 2012, 05:08PM

Registered Member #4037 Joined: Fri Jul 29 2011, 03:13PM
Location:
Posts: 86

If you are going to use swappable heads in the same job, the alignment of the nozzles would have to be better than the accuracy that you are trying to accomplish. Otherwise, you'll risk having the different materials offset from each other.

This doesn't sound like the type of things that you can do without some good alignment mechanisms with locking mechanism. Sort of like those snap on tools. Steppers doesn't have a position feedback mechanism, so whatever the amount of force you can use without "slipping" is limited by the motors.

What about a larger piece that you can pre-assemble multiple heads like those weapon pods on a fighter. The software would compensate for the known physical offsets for the head it want to use.

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